Optical RZ signals are becoming increasingly important in optical communication systems. They have proven to be superior to the non-return-to-zero (NRZ) format both in terms of receiver sensitivity, which is discussed in S. D. Personick, “Receiver design for digital fiber optic communication systems I”, Bell Syst. Tech. J., vol. 52, 843–874 (1973), L. Boivin et al., “Receiver sensitivity improvement by impulsive coding”, IEEE Photon. Technol. Lett. vol. 9, no. 5, 684–686 (1997), W. A. Atia et al., “Demonstration of return-to-zero signaling in both OOK and DPSK formats to improve receiver sensitivity in an optically preamplified receiver”, Proc. IEEE LEOS'99, TuM3, and P. J. Winzer et al., “Sensitivity enhancement of optical receivers by impulsive coding”, J. Lightwave Technol. vol. 17, no. 2, 171–177 (1999), and in terms of fiber transmission performance, which is discussed in D. Breuer et al., “Comparison of NRZ- and RZ-modulation format for 40-Gb/s TDM standard-fiber systems”, IEEE Photon. Technol. Lett., vol. 9, no. 3, 398–400 (1997), R. Ludwig et al., “Experimental comparison of 40 Gbit/s RZ and NRZ transmission over standard single mode fibre”, Electron. Lett., vol. 35, no. 25, 2216–2218 (1999), and in C. Caspar et al., “RZ versus NRZ modulation format for dispersion compensated SMF-based 10-Gb/s transmission with more than 100-km amplifier spacing”, IEEE Photon. Technol. Lett., vol. 11, no. 4, 481–483 (1999). The two most commonly used techniques to generate optical RZ data streams either employ a sinusoidally driven intensity modulator or an actively mode-locked laser, as described, for example, in A. Ougazzaden et al., “40 Gb/s tandem electro-absorption modulator”, Proc. OFC'01, PD14 (2001), R. A. Griffin et. al., “Integrated 10 Gb/s chirped return-to-zero transmitter using GaAs/AlGaAs modulators”, Proc. OFC'01, PD15 (2001), and H. Suche et al., “Integrated optical Ti:Er:LiNbO3 soliton source”, IEEE J. Quantum Electron., vol. 33, no. 10, 1642–1646 (1997), in addition to a NRZ data modulator. Apart from the need for two or more high-power RF components, these techniques necessitate accurate synchronisation between the data modulator and the pulse source. Two less frequently used techniques make use of electrical RZ generation by means of gating the NRZ clock with the NRZ data signal (see N. M. Froberg et al., “Generation of 12.5 Gbit/s soliton data stream with an integrated laser-modulator transmitter”, Electron. Lett., vol. 30, no. 22, 1880–1881 (1994) or drive a Mach-Zehnder intensity modulator with the NRZ data between its transmission minima (see J. J. Veselka et al., “A soliton transmitter using a cw laser and an NRZ driven Mach-Zehnder modulator”, IEEE Photon. Technol. Lett., vol. 8, no. 7, 950–952 (1996)).